This invention relates to a method for fabricating gravure printing cylinders with a synthetic resin surface, having excellent engraving quality, wear resistance, and solvent resistance.
In recent years, with developments in electronics, automatic and precise etching of gravure cylinders by means of electronic engravers is coming into wide practice.
In addition to the conventional gravure cylinders entirely made of metal, gravure cylinders with a printing surface made of synthetic resin are entering into this field.
Heretofore, for making gravure cylinders, wide use has been made of the so-called "conventional" method, which comprises the steps of plating a copper layer over a cylindrical base, placing an exposed carbon tissue having a latent image over the copper layer, developing the carbon tissue, etching the cylinder through the carbon tissue, thereafter stripping the tissue from the layer, and chromium plating the tissue-stripped cylinder. This method involves pollution problems since it includes chemical treatment processes, such as plating and etching processes, and further, the method necessitates highly skilled art and labor for forming gravure cells as the etching is made by the use of the carbon tissue.
The electronic engraver simplifies the etching process, and the formation of the printing surface with resin eliminates the plating processess. On these points, the method of fabricating gravure cylinders in which the resin coated over the printing surface is engraved by an electronic engraver is being developed as an excellent method for making gravure printing plates.
However, such resin-coated gravure printing cylinders are inferior in productivity and have not yet satisfied the requirements for the gravure printing, such as engraving quality, wear resistance, and solvent resistance.
Conventionally, vinylchloride resins, ABS resins, aliphatic polyamide resins, and the like are used for the gravure cylinder coating. With respect to polyamide resins, an alcohol-soluble polyamide such as copolymer nylon, and modified nylon can be dissolved in a solvent and caused to adhere to a cylindrical base by a method called the blade coater method but has very low solvent resistance against the gravure ink. On the other hand, nylon 6, 66, 610, 11, 12 and the like have solvent resistance, but it is difficult for these resins to be dissolved in a solvent to be coated over the gravure cylinder. Under the existing circumstances, with respect to the polyamide resin, the use of the plastic molding method utilizing its thermoplasticity and powder coating method is being tried. These methods, however, necessitate rather large apparatus and have further disadvantages in the production of the gravure cylinder such as the necessity of surface smoothing by means of a super-precision lathe after adhesion of the resin.
Vinylchloride resin can be also caused to adhere to the cylindrical base by the above mentioned blade coater method but requires degassing and surface smoothing processes. Further, the finished coating has low solvent resistance and accordingly is greatly restricted in the printing conditions such as the use of water-base gravure ink.
In addition, all gravure printing cylinders with printing surfaces made of the foregoing resins by the aforementioned methods have relatively low wear resistance. That is, the gravure printing cylinders are easily scratched by impurities in the ink and on the doctor blade, dust and the like, almost all cylinders being damaged during printing of web of less than 10,000 meters long, and it is difficult to apply these cylinders to large lot printing of more than 100,000 meters long. In the attempt to improve the wear resistance, the doctor blade is being made of synthetic resin but is inferior in edge accuracy, edge machining property, ink scraping property, etc., and lacks utility.
The foregoing synthetic resins also have inferior engraving property. More specifically, the engraving of the pattern of an original by the engraving needle is likely to produce burrs and breaks around the cells. Since such burrs can be the cause of scumming, a knife called a burr cutter is provided in the electronic photoengraving machine for scraping away the burrs. However, the operation of the burr cutter can cause the smooth surface of the non-image area to suffer scratches, and thus a burr cutter itself becomes a cause of scumming.
Accordingly, it is desirable that the resin layer has an engraving property which makes a burr cutter unnecessary.